Spark plug construction



Oct. 19, 1954 R, J. L. DUTTERER SPARK PLUG CONSTRUCTION Filed Sept. 21,1951 MGM IN VEN TOR. %6/i M16. /a//z/ e/ Patented Oct. 19, 1954 SPARKPLUG CONSTRUCTION Rex 3. L. Dutterer, Hastings, MiclL, assignor toHastings Manufacturing Company, Hastings,

Mich.

Application September 21, 1951, Serial No. 247,600

9 Claims.

This invention relates to improvements in spark plug construction.

This application is a continuation in part oi my copending applicationfor Spark Plug and Method of Manufacture Therefor, Serial No. 728,421filed February 14, 1947, Patent Number 2,634,716 issued April 14, 1953.

The principal. objects of this invention are:

First, to provide a spark plug which is particularly easy to assemble.

Second, to provide a spark plug which can be manufactured with variedbut accurately controllable operating characteristics.

Third, to provide a spark plug which is particularly durable, especiallyin the performance of its central seal and current conducting elements.

Fourth, to provide a novel form of seal and electrical connectionbetween the sections of a sectional center electrode of a spark plug.

Fifth, to provide a spark plug in which the center insulated electrodemay be formed of inexpensive base metals without endangering the seal ofthe center electrode or the insulator to breakage.

Sixth, to provide a coiled metallic intermediate connector between thesections of a sectional electrode, which connector forms a positive andcontinuous electrical connection between the electrode sections andwhich is protected and restrained against deterioration and movement bya solidified seal that also seals the central bore of the insulator inwhich the electrode is mounted.

Other objects and advantages of my invention will be apparent from aconsideration of the following description and claims.

The drawings, of which there is one sheet illustrate a highly practicalform of my spark plug.

Fig. 1 is an elevational view of the completed spark plug.

Fig. 2 is a longitudinal cross-sectional view through the insulator ofthe spark plug illustrating the center or insulated electrode inelevation.

Fig. 3 is an enlarged fragmentary cross-sectional view through theinsulator and center elec-- trode of the spark plug in finishedassembled condition.

Fig. 4 is an enlarged fragmentary longitudinal cross-sectional viewthrough the insulator illustrating the sections of the center electrodein partially assembled position within the insulator.

Fig. 5 is an enlarged fragmentary elevational view of the lower sectionof the center electrode with the spiral intermediate connector mountedthereon.

Spark plug manufacturers have recognized for some time that differentinternal combustion engines require spark plugs having differentoperating characteristics. Not only must the insulated center electrodeof the spark plug provide continuous electrical contact for the passageof ignition current therethro-ugh and be sealed to the insulator toprevent the escape of combustion gases along the center electrode, butthe center electrode must dissipate heat through the insulator of thespark plug at different predictable rates in order that the temperatureof the inner tip of the center electrode will remain at the desiredlevel during operation. A spark plug which does not dissipate sufiicientheat from its center electrode may become so overheated in some enginesas to cause pre-ignition. Such a plug is designated as a hot plug. Aplug which dissipates a large amount of heat from its center electrodewill have an inner tip that is so cool in some engines that partiallyburned fuel and oil collects on the tip and fouls the plug. Such a plugis designated as a cold plug. My present invention is directed towardproviding a standard form of spark plug having standardized majorelements which can be easily and inexpensively manufactured andassembled to have predeterminable operative characteristics ranging fromthe above described hot plugs to cold plugs.

Fig. 1 illustrates the principal elements of my plug which includes aninsulator of insulating ceramic material retained within a metallicsleeve 2. The sleeve 2 is provided with a nutlike head 3 and a threadedinner tip 4 for mounting the same in an engine as is common practice.The sleeve carries a grounded electrode '5 that cooperates with a centeror insulated electrode extending through the insulator. The insulatedelectrode includes an inner tip 6 cooperative with the groundedelectrode, and an outer terminal tip 7 adapted to receive a connectorwire from the distributor of an engine.

As is more particularly illustrated in Fig. 2 the insulator l includes acentral portion 8 of thickened cross-section or diameter and a taperedinner end 9 that extends inwardly through the tip 4 of the sleeve.Throughout this description the elements of the spark plug will beoriented by reference to their usual position with respect to thecylinder of an engine. Thus the tip of the insulated electrode 6 isdisposed inwardly of the cylinder, while the terminal 1 is disposedoutwardly of the cylinder. The insulator l defines a center bore I0extending therethrough, the bore being provided with a threaded portionil which is desirably positioned entirely within the thickened portion 8of the insulator. Inwardly of the threaded portion i I the bore 19provides a cavity l2 which is also located within the thickened portionii of the insulator. The inner end of the cavity I2 terminates in aninwardly tapered shoulderJS merging with an inner portion 14 of thecentral bore of reduced diameter.

The insulated center electrode of the spark plug includes an outerrod-like section IE on which the terminal tip I is formed. The inner endof the outer section i5 is threaded as at is to threadingly engage thethreaded portion ll of the insulator. It is pointed out that the threadsin the insulator bore are of substantially greater diameter than thethreads on the outer electrode section so, that a loose engagement isobtained between the threaded elements. A collar IT on the outer end ofthe outer electrode section en.- gages the outer end of the insulator tolimit the movement of the outer electrode section into the insulator.

The inner tip 6 of the insulated; electrode consists of the inner end ofa pin-like inner electrode section 18 that extends through the reducedportion I4 of the central bore in the: insulator. The inner electrodesection is provided with a collar 19 having an inwardly tapered underedge 29 which seats upon the tapered shoulder l 3 at the bottom ofthecavity 12in the insulator. Aboye the collar [9 the inner electrodesection is plovided with an outwardly extending centering projection 2|.It will be noted from Figs. 2 and 3 that the inner end of the outerelectrode section i8 is spaced substantially from the outer end of thecentering projection 2| in the assem' bled positions of the electrodesections.

Electrical continuity in the insulated electrode is provided between theinner electrode section if; andthe outer electrode section by a spirallycoiled metallic connector section 22; The spiral connector 22 isguidingly received around the centering projection 2l of the innerelectrode sectipn and projects outwardly therefrom. It is desirable thatthe gauge of wire used in the spiral connector and the diameter of thecentering projection 2| be such that the spiral connector 22 is spacedsubstantially inwardly from the walls of the cavity l2 as illustrated.In its uncompressed condition the spiral connector 22 projects outwardlysubstantially beyond its final position as will be noted by a comparisonof Figs. 3 and 4. The outer electrode section-is providedwith a taperedinner end 23 which centeringlyengages the outerend of the spiralconnector-as the outer; electrode section is threaded intothe insulator,and compresses the spiral connector into positive electrical contactwith each of 1 the innerand outer electrode sections. The compression inthe spiralconnector- 22 also serves to firmly seat the inner electrodesection within the bottom of the cavity I2.

In assembling the above described standard elements of my spark plug Iprefer to fit the spiral connector 22 on thecentering projection 2| onthe inner electrode section, and drop thetwo elements as a sub-assemblyinto the bore of the insulator. Desirably the spiral connector hassufficient gripping engagement with the projection 2| soas not to becomedisengaged therefrom. After the inner electrode section and spiralconnector are in place I inject a predetermined and measured amount of asemi-fluid or plastic sealing material 24 into the cavity l2-and aroundthe connector 22; The sealingmaterial is desirably a chemically settingceramic cement including a silicate. of soda binder, andv desirably hasa. coefiicient of expansion approximating the coefiicient of expansionof the insulator 1, although this is not of great importance, as thesealing material is located within the thickened portion 8 of theinsulatorwhere the insulator has the greatest strength andv ability toresist any tendency of the sealing material to crack the insulator.

After the sealing material 24 is in place the outer electrode section I5is threaded into the insulator as above described to contact andcompress the spiral connector 22. In so doing the inner tip of the outerelectrode section wipingly engages the outer end of the spiral connectorin a rotary motion to obtain good electrical con- 4 tact therewith. Theinner tip of; the outer electrode section also penetrates and displacesa quantity of the sealing material 24 upwardly between the looselyengaged threads on the insulator and the outer electrode section as isindicated at 25 in Fig. 3.

The amount of sealing material thus displaced and forced upwardly in theinsulator bore is of course determined by the quantity of sealingmaterial originally introduced into the cavity l2. Thepresence of thesealing material between the insulated center electrode and the wall ofthe insulator of course increases the rate of radiation of heat from theelectrode to the insulator, and by increasing the amount of sealingmaterial and thedistance through which it rises along the threads II Iam able to increase the rate of heat dissipation from the spark plug.Thus a great amount of sealing material provides a cooler spark plug,While the reduced amount of sealing material provides a hotter sparkplug. It will be noted that the penetration of the outer electrodesection into the sealing material also forces the sealing materialuniformly around the outer end of the inner electrode section and thespiral connector 22.

It will be noted that the inner electrod is of such a diameter thatthere is substantial clearance between it and the wall of the bore belowthe shoulder. The beveled shoulders of the bore and of the innerelectrode section result in an effective centering of the innerelectrode section in the bore and also close engagement to insure thatthe sealing material i not forced between the shoulders and between thebody portion of the inner electrode and the insulator bore which shouldbe kept free from the sealing material. The intermediate electrodesection being of springable material, such as the coil springillustrated, forces the connecting shoulders together when the outerelectrode section is threaded into engagementwith the internal threadsof the insulator bore and this also insures a good electrical conductingcontact between the intermediate and inner and outer electrode sections.

The sealing cement embeds the portion of the inner electrode sectionabove the shoulder of the bore and keeps the inner electrode centered.It also embeds the intermediate electrod section and the lower end ofthe outer electrode section so thatno relative movement of these partscan take place after the sealing cement has set. As stated,aself-setting sealing mixture is desirably used. which eliminates thenecessity for applying heat to set the sealing mixture. The looseengagement of the outer electrode sectio with the threads of theinsulator bore is desirable not only from the standpoint of tolerancesin manufacture and difficulty in securing accurate threads in the moldedinsulator body but it also permits the. sealing mixture forming aneffective seal between. the outer electrode and the insulator andinsuresthat the outer electrode is effectively retained.

Attention is called to the fact that the dimensions of the insulator,theinner electrode section, and the outer electrode section are notparticularly critical to the performance of the finished spark plug, asthe performance is controlled largely by the amount of sealing materialin the plug. It is therefore possible to economically manufacture the.standardized elements of the plug within reasonably accurate limits, andwithoutexpensive tolerance controls and inspections. s emb o the. men tha -l1; l s s.

relatively simple and can b carried out without the use of heat orexpensive jigs and apparatus.

Having thus described my invention, What I claim as new and desire tosecure by Letters Patent is:

1. A spark plug comprising an insulator having a central boretherethrough, said bore having an inner portion of reduced diameter withan outwardly facing beveled shoulder around the outer end thereof, saidbore being internally threaded in outwardly spaced relation to saidshoulder, an inner electrode section disposed in the reduced portion ofsaid bore and having a beveled shoulder seated upon the outwardly facingshoulder of said bore, the diameter of the inner electrode being suchthat there is substantial clearance between'it and the bore below thesaid shoulder, the said inner electrode section having a centeringprojection extendnig outwardly from its said shoulder and spaced fromthe wall of the bore, a coiled initially springable metallicintermediate electrode section having its inner end sleeved upon saidcentering projection and centered thereby, an outer electrode sectionhaving loose threaded engagement with the threads of said bore andcompressibly engaging the outer end of said springable intermediatesection and urging the shoulder of said inner section upon said beveledshoulder of said bore and centering the inner section in the reducedportion of said bore, and a self-setting cementatious mixture fillingthe said bore between said inner and outer sections and embedding saidintermediate section, said mixture surrounding the inner end of saidouter section and extending I outwardly between at least a portion ofthe threads of the outer section and the bore.

2. A spark plug comprising an insulator having a central boretherethrough, said bore having an inner portion of reduced diameter withan outwardly facing shoulder around the outer end thereof, said borebeing internally threaded in outwardly spaced relation to said shoulder,an inner electrode section disposed invthe reduced portion of said boreand having a shoulder seated upon the outwardly facing shoulder of saidbore,

the said inner electrode section having a centering projection extendingoutwardly from its said shoulder and spaced from the wallv of the bore,a coiled initially springable metallic intermediate electrode sectionhaving its inner end sleeved upon said centering projection and centeredthereby, an outer electrode section having loose threaded'engagementwith the threads of said bore and compressibly engaging the outer end ofsaid springable intermediat section and urging the shoulder of saidinner section upon said shoulder of said bore, and a self-settingcementa tious mixture filling the said bore between said inner and outersections and embedding said intermediate section, said mixturesurrounding the inner end of said outer section and extending outwardlybetween at least a portion of the threads of the outer section and thebore.

3. A spark plug comprising an insulator having a central boretherethrough, said bore having an inner portion of reduced diameter withan outwardly facing beveled shoulder around the outer end thereof,saidbore having internal projections in outwardly spaced relation tosaid shoulder, an inner electrode section disposed in the reducedportion of said bore and having a shoulder seated upon the outwardlyfacing shoulder of said bore, the diameter of the inner electrode beingsuch that there is substantial clearance between it and the bore belowthe said shoulder, the said inner electrode section having a centeringprojection extending outwardly from its said shoulder and spaced fromthe wall of the bore, a coiled initially springable metallicintermediate electrode section having its inner end sleeved around saidcentering projection and centered thereby, an outer electrode sectionhaving projections coacting with the projections of said bore in axiallyoverlapping relation, said outer electrode section compressibly engagingsaid springable intermediate section and urging the shoulder of saidinner section upon said shoulder of said bore and centering the innersection in the reduced portion of said bore, and a sealing mixturefilling the said bore between said inner and outer sections andembedding said intermediate section.

4. A spark plug comprising an insulator having a central boretherethrough, said bore having an inner portion of reduced diameter withan outwardly facing shoulder around the outer end thereof, said borehaving internal projections in outwardly spaced relation to saidshoulder, an inner electrode section disposed in the reduced portion ofsaid bore and having a shoulder seated upon the outwardly facingshoulder of said bore, the said inner electrode section having acentering projection extending outwardly from its said shoulderandspaced from the wall of the bore, a coiled initially springablemetallic intermediate electrode section having its inner end engagedwith said centering projection and centered thereby, an outer electrodesection having projections coacting with the projections of said bore inaxially overlapped relation, said outer electrode section compressiblyengaging said springable intermediate section and urging the shoulder ofsaid inner section upon said shoulder of said bore, and a sealingmixture filling the said bore between said inner and outer sections andembedding said intermediate section.

5. A spark plug comprising an insulator having a central bore formedtherethrough and having a thickened intermediate section adapted to bereceived in a metal shell, said bore having an inner portion of reduceddiameter with an outwardly facing shoulder around the outer end thereofand located within the thickened intermediate section of the insulatorand substantially inwardly from the outer end of said thickened portion,threads formed around a portion of said bore and spaced outwardly fromsaid shoulder and within the thickened portion of the insulator, aninner electrodev section projecting through the inner reduced portion ofsaid bore and having a collar seated against said shoulder, a centeringprojection on said inner electrode section extending outwardly from saidcollar and spaced from the wall of said bore, an outer electrode sectionextending into said bore from the outer end thereof, the inner end ofsaid outer electrode section being spaced from said centeringprojection, a coiled metallic connector section sleeved around saidcentering projection and compressed between the collar on said innerelectrode section and the inner end of said outer electrode section,said connector being spaced from the wall of said bore, threads formedaround said outer electrode section and engaging the threads in saidbore, the threads in said bore being of greater diameter than thethreads on said outer electrode section whereby a loose threadedengagement is obtained therebetween, and a sealing mixture including a2,091 ,QY-Eli chemically setting cement. filling; said bore be-- tween;said; inner and outer electrode-sections and surrounding said connectorsectiomsaidseale ing mixture extending outwardly between the;

threads on said outer electrode section; and the threadsin said bore.

6. A spark plug comprising an insulator having acentralbore-formed-therethrough and having a thickened intermediatesectionadapted to:-b.e; received in a metal shell, said borehaving antion projectingthrough the inner reduced portion.

of said bore and having a collar seated. against. said shoulder; acentering projection on said inner electrode section extending outwardlyfromsaid collar and spaced from the wall of said bore, an-

outer electrode section extending intosaid. bore. from the outer endthereof and having a. collar engaging the outer end of said insulator,the

inner end of said outer.v electrode. section being,

tapered and spaced'from said centering. projection, a coiled metallicconnector section sleeved around said centering projection andcompressed.

between the collar on said inner electrode section;

and the inner tapered end of said outer electrode section, saidconnector beingspaced from the wall.

of said bore, radial serrations formed around said outer electrodesection and engaging the serrations in said bore, the serration in saidbore being of greater diameter than the. serrationsonsaid outerelectrode section whereby a loose.inter.-

locking engagement is obtained therebetween,.

and a sealing mixture including a chemically setting cement filling saidbore between said inner and outer electrode sections and surroundingsaid connector section, said sealing mixture extending outwardly betweenthe serrationson said outer. electrode section and the serrationsin saidbore.

7. A spark plug comprising an insulator having a. central bore formedtherethrough, said bore having an inner portion of reduced diameter withan outwardly facing beveled shoulder around the outer end thereof,radial serrations formed around a portion of said bore andspacedoutwardly from said shoulder, an inner electrode sectionprojecting through the inner reduced portion. of saidbore andv havingacollar seated against said shoulder, a centering projection on saidinner electrode section extending outwardly from said collar and spacedfrom thewall of said bore, an outer electrode section extending intosaid bore from the outer end thereof and having a collar engaging theouter end of said insulator, the inner end of said outer electrodesection being tapered and spaced from said centering projection, acoiled metallic connector section sleeved.

around said centering projection and compressed between .the collar onsaid inner electrode section' and the inner tapered end of said outerelectrode section, said connector being spaced from the wall.

of said bore, radial serrations formed around said outer electrodesection and engaging the serrations in said bore, the serrations in saidbore being of greater diameter than the serrations on said.

outer electrode section whereby a loose interlocking engagement isobtained therebetween, andv a sealing mixture. including; a. chemicallysetting cementfilling saidrbore between saiduinner' andiouter electrodesections: andsurrounding. said' connector section; .saidsealingmixture extending outwardly between the serrations on said: outerelectrode section and the serrations in saidbore.

8; A spark plugcomprising an insulator having a central bore formedtherethrough, said bore havingan inner portion of reduced diameter withanoutwardlyfaoing; shoulder around the outer end thereof, axially spacedradial projections formed alonga portion of said bore and spacedoutwardly. from said shoulder, an'inner electrode section proj ecting.through 'theinner reduced portionv of said bore and having a collarseated against said shoulder, a centering projection on said innerelectrode sectionwextending outwardly from-said-collar and spaoedfrom.the wall of said bore, an outer electrode sectionextending into saidbore from the outer end thereof and having a collar engaging'theouter-endof said insulator, the'innerrend'ofisaid outer. electrodesection being spaced from saidcentering projection, a coiled metallicconnector. section sleeved around said centering projection andcompressed between the collar onsaid inner. electrode section and theinner end ofsaidouter electrode section, said connector being spacedfrom the wall of said bore;.radially projecting ribs'formed around saidouter electrode section and. spaced between the projections insaid'bore' in axially overlapping relation; anda sealing mixtureincluding a chemically setting; cement filling said bore between saidinner and outer electrode sections and surrounding said connectorsection, said sealing mixture extending outwardly between the ribson-said outer electrode section and the 'projectionsin said bore.

9. A spark'plugr comprising; an-insula-tor having a central: boreformed: therethrough, saidbore having aniaxially inner portion ofreduced-diam-- eter', axially spaced radial: projections formed along-aportion of 'said'bore and spacedoutwardly from said-reduced: portion: ofsaid vbore, an inner electrode section projecting: through the innerreduced portion of said'bore andseating therein, a centeringprojection.on. said inner electrode section extending outwardly from said reducedportion'of' sa-id'bore, an outer electrode'section extending into saidbore from the outer end there-- of and havingacollar; engaging the outerend of said insulator, the inner 'end of :said: outerelectrode-sectionbeingtapered and spaced from said centering projection;a coiledmetallic connector section'jsleeved. aroundfsaid centeringprojection and compressedbetweensaidiinner electrode.section and theinner taperedend-ofsaid-outer electrode section, said connector beingspaced from.

the wall of said bore; radial ribsformed around. said outer electrodesection and. positioned.between the projections in said here in axiallyover= lapping relation, and asealing mixture including a chemicallysetting cement filling said bore between said inner and outer electrodesections and:

surrounding said connector'section', said sealing mixture extendingoutwardly'between the ribs on said outer electrode section andtheprojections in said bore.

References, Cited in the file of this patent.

UNITED "STATES PATENTS Number Name Date 2,071,571 Rabezzanazet' a1: Feb;23; 1937 2,246,948 McCarty-etal -June 24, 19.41. 2,317,305Schwartzwalderet a1; Apr. 20,1943 2353348 Tognola etal ..Nov; 2, 19482

